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Have you checked Google Webmaster Central to see if there is any information on the domain there? Does your website still show up for other keywords? Does the page that was ranking for 'domain sales' still show when you perform a 'site:www.example.org' query for your domain? Have you recently engaged in any shady or black hat SEO activities that might have caused a penalty for this page? Has the page been ranking top 10 for a long amount of time?